The present invention relates to a treatment apparatus for preserving pumpable food products in a pulsed electric field, said apparatus comprising a treatment chamber with an inlet for food products to be treated and an outlet for treated food products, the treatment chamber being provided with a system of electrodes which comprises at least one first electrode and at least one second electrode, as well as an electrical energy source connected to the electrodes and a potential controller to control a potential on at least one first electrode and on at least one second electrode in order to generate a pulsed electric field.
A treatment apparatus of this type is known in the art, for example from the U.S. Pat. No. 4,457,221. In this known apparatus, a treatment of food products in a pulsed electric field (sometimes abbreviated in the art to PEF (Pulsed Electric Field) treatment) is carried out in order to destroy microorganisms such as spores, bacteria, moulds, yeasts and the like which are present in the food product and thus to extend the shelf life of the food products. Electroporation is the process which is assumed to occur in the microorganisms and thus to have a lethal effect on these. Compared with customary preserving treatments such as sterilization, pasteurization under the influence of heat, the treatment in a pulsed electric field has the advantage that no significant increase in temperature of the product occurs, which has a beneficial effect on the colour, texture, taste and the like of the food products.
One of the embodiments of a treatment apparatus disclosed by U.S. Pat. No. 4,457,221 consists of a treatment chamber which comprises an elongate cell having an inlet for products to be treated and an outlet for the treated products, wherein parallel plate electrodes, which are connected to a suitable current source and pulse generator and are driven thereby, are disposed along the two lateral walls which face one another. Owing to the fixed spacing between the parallel electrodes and the uniform charge density (per unit area) the strength of field E is constant, apart from those areas which border the ends of the plate electrodes. With this known apparatus there is the risk, however, that undesirable contaminants, for example dead matter, will accumulate in the corners of the container, this being a possibility, in particular, in the case of inhomogeneous food products.
In the case of another known PEF technique, as described, for example, in U.S. Pat. No. 5,690,978, the electrodes are disposed not opposite one another, but behind one another, in the flow direction of the product, and are separated by an insulator, for example as components of a round tube. The field lines of the electric field thus run substantially parallel to the flow direction. The magnitude of the electric field, measured in a plane perpendicular to the flow direction, and the magnitude in the longitudinal direction, are not the same everywhere, however, thus giving rise to a temperature gradient in the product, which temperature gradient in turn causes a change in the conductivity in the flow direction, as a result of which the field strength becomes even more inhomogeneous. A uniform product treatment is therefore difficult to achieve with this embodiment of the PEF technique.
Yet another treatment apparatus known in the art employs concentrically disposed electrodes, the product being guided into the annular gap between the electrodes and being subjected to a radially directed electric field. A drawback of this design, apart from its complexity, is the relatively small flow passage, as a result of which solid particles in a food product (eg. forcemeat balls in soup) may cause problems.
It is an object of the present invention to avoid the problems of the prior art apparatuses and methods outlined above.
More particularly, it is an object of the present invention to provide a uniform electric field across the effective area of flow of the treatment apparatus and in the longitudinal direction thereof, so that food products can be subjected to a uniform preserving treatment.
To this end, the treatment apparatus of the abovementioned type according to the invention is characterized in that the treatment chamber has an effective area of flow having rounded corners and the at least one first electrode and the at least one second electrode of the system of electrodes are disposed in such a way that the field lines of the electric field run parallel to one another and the potential controller is of such design that the electric field in the effective area of flow is uniform.
In the treatment apparatus according to the invention, the treatment chamber has an effective area of flow (i.e. perfused treatment-chamber area perpendicular to the flow direction) without corners or alternatively with rounded corners, so that no contaminants and the like can accumulate on the walls. Examples of such effective areas of flow are a circle and an ellipse. The first electrode(s) and the second electrode(s) are disposed in such a way that the field lines of the electric field generated during operation of the apparatus run substantially parallel to one another, in contrast to the radial field in the last-discussed PEF apparatus according to the prior art. In addition, the controller for the potential on the electrodes is of such design that the electric field in the effective area of flow is uniform. In other words, the magnitude and direction of the electric field are at all times constant in a plane perpendicular to the flow direction. As a result of the uniform electric field, the food products are subjected to a uniform preserving treatment.
The potential on an electrode disposed at a distance ij from a reference plane, said reference plane being perpendicular to the field direction, is governed by the general formula V(ij)=E.ij.